Organic semiconductors based on molecular and polymeric materials have been in wide use in electronics industry for the last 30 years as a complement to the shortcomings of inorganic semiconductors. Importantly, organic semiconductors offer, when compared to the inorganic-based technology, greater ease in device processability, flexibility, substrate compatibility, and reduced cost; as well as facile tuning of the frontier molecular orbital energies by molecular design.
Field-effect transistor (FET) is a key device used in the electronic industry, which is based on inorganic electrodes, insulators, and semiconductors. FETs based on organic semiconductors (OFET) are finding its applications in low-performance memory elements as well as in integrated optoelectronic devices, such as pixel drive and switching elements in active-matrix organic light-emitting diode (LED) displays.
Earlier attempts from other research groups at incorporating perylenebisimide (PBI) into devices included chemical vapor deposition which is a highly costly process and not all small molecules can be fabricated into devices by this method. Mono- and diimideperylene and naphthalene compounds, N- and core-substituted with electron-withdrawing groups, for use in the fabrication of various device structures are disclosed in U.S. Pat. No. 7,671,202.
Organic field effect transistors (OFETS) operable in p-type mode are more well-known compared to n-type ones. Among the few n-type organic semiconductors used, those based on diimides like perylene or naphthalene diimide are the most investigated ones. However, such compounds have been found to have issues of insolubility which make them unfavorable in device fabrication.
An alternate method involves the transesterification of perylene bisimide derivatives with polymers so as to obtain spin coatable films, but this method also suffered from phase separation problems.
Other methods of developing Perylenebisimide based main chain homopolymers and copolymers, have also not been very successful as they are usually highly rigid, insoluble and low-molecular weight materials which cannot form free-standing films.
Article titled “Mechanistic Aspects of Ester-Carbonate Exchange in Polycarbonate/Cycloaliphatic Polyester with Model Reactions” published 16 Mar. 2004 by M. JAYAKANNAN discloses reactive blending of bisphenol A polycarbonate (PC) with poly(1,4-cyclohexanedimethylene-1,4-cyclohexanedicarboxylate) (PCCD).
Article titled “Molecular semiconductor blends: Microstructure, charge carrier transport, and application in photovoltaic cells” [Phys. Status Solidi A 206, No. 12, 2683-2694 (2009)] disclose blends of two electroluminescent materials oligothiophene and a perylene derivative which are useful as light-emitting OFETs.
Article tided “Sequestration of electroactive materials in a high Tg, insulating polymer matrix for optoelectronic applications. Part 2. Photovoltaic devices” Jiang et. al in Polymer, vol. 47, pp. 4124-4131(2006)]. incorporation of high levels of electroactive compounds into a high Tg matrix polymer and combination of electron donor-electron acceptor pairs with optionally light harvesting organics (e.g. laser dyes) in the high Tg polymer matrix yielded Photovoltaic (PV) performance in the range of literature data typically reported for organic based PV devices.
In light of the above, it is an object of the present invention to provide n-type semiconductor compounds and process for preparation and methods of their use, that overcome various deficiencies and shortcomings of the prior art outlined as above. While various copolymers of PBI with other molecules such as oligothiophene and the copolymer of PCCD with polycarbonate are known in the art, however, the transesterification of PCCD with PBI is hitherto undisclosed.